In supplying various utilities to a home, it is frequently desired that metal objects be connected to a suitable electrical ground or that a grounding wire be connected to a metal object which is already properly grounded. Such a ground connection is desirable because it can protect an individual or machine from serious harm in the event of a short circuit or other fault condition. Typically, a variety of clamping devices have been employed to accomplish the desired connection.
As is known in the art, these clamping devices can take the form of a U-shaped clamping device which can be secured to an object by placing the object at least partially within the U-shaped portion of the device and tightening a threaded stud member carried by the U-shaped portion against a generally flat surface of the object. A ground wire is then connected to the clamping device.
Ideally, a clamping device used as discussed above should possess several attributes. First, the device components themselves must be able to withstand the potentially high currents that can be encountered under some fault conditions. Second, the device must be able to effect an adequate physical and electrical connection between the ground wire and clamped object. Third, the clamping device must be of a design that will maintain a sound physical and electrical connection after prolonged use. Finally, the clamp must be simple and economical to construct and install.
Until now, clamping devices known in the art have not simultaneously possessed all these desirable attributes.
For example, the need for adequate physical and electrical contact between the clamped object and the clamping device suggests that the threaded stud member should be physically hard enough to penetrate or abrade the surface of the clamped object and any protective coating applied thereto. Ideally, the stud means could be constructed of a physically hard metal such as steel to accomplish this purpose. Unfortunately, steel has a relatively high electrical resistivity. Metals possessing a high electrical resistivity can heat up, deform or self-destruct when high electrical currents pass through them. Thus, a steel stud portion could overheat, distort, or be destroyed under the potentially high current conditions encountered in grounding applications. This in turn can reduce the clamping device effectiveness or destroy the clamp completely.
Alternatively, the stud could be constructed from copper or a copper alloy such as bronze having a low electrical resistivity. This would ensure that the stud could successfully carry the potentially high currents encountered under fault conditions. However, copper and bronze are physically soft metals. Therefore, a copper or copper alloy stud would not be physically hard enough to penetrate or abrade the clamped object's surface, thereby failing to effect adequate mechanical and electrical contact with the clamped object.
Differing electrochemical properties of the ground wire, object to be clamped and clamping device components can also compromise the operation of the clamping device. For example, when a copper or bronze stud is used in a clamping device which is clamped to a steel object, galvanic corrosion products can occur at the copper-steel interface. This problem is especially acute where, as in this case, the surface area of the dissimilar metal junction is relatively small. The galvanic corrosion products formed under these conditions can degrade the electrical efficiency of the clamping device, physically alter the clamped object and the clamping device components, and make removal of the clamping device difficult.